The present invention relates to a chain saw device including a self-contained cassette adapted for installation on a chain saw, and particularly to a cassette which can be easily and quickly installed or removed from the chain saw.
A saw chain cassette typically includes a saw bar having a peripheral groove for guiding a saw chain adapted to be driven by a drive sprocket also incorporated into the cassette. The cassette is attached to the frame of a chain saw as a unit and is replaced as a unit thereby avoiding the necessity for removing an old chain from a saw bar and replacing the same with a new chain in proper entrained relationship with the saw bar and sprocket, the latter task being time consuming and requiring a degree of skill. However, prior cassettes are usually bolted to the chain saw frame in a manner similar to the mode of attachment of a conventional saw bar, and unless a number of bolts are employed the cassette is apt to wobble in a vertical direction during use, i.e. in a clockwise or counterclockwise direction with respect to the driving motor shaft. Furthermore, the saw bar sprocket, even though a part of the cassette, often is secured to the chain saw motor shaft employing a threaded connector or the like. Therefore even the installation of a cassette has been somewhat time consuming.
Moreover in a cassette configuration the sprocket is usually movable along the cassette saw bar so as to permit proper adjustment in the tensioning of the chain. The riveted connections of the chain tend to become loose with age whereby the chain actually appears to increase in overall length. The proper tension must be maintained in order that the chain will properly track around the saw bar and over the sprocket rather than becoming loose and behaving erratically or even slipping off the saw bar. Although the saw bar of the conventional cassette is releasably bolted to the chain saw and may be periodically unbolted and adjusted in such a manner that the proper saw chain tension is achieved, nevertheless when the cassette is removed from the chain saw or temporarily stored the sprocket is free to move relative to the bar and the chain can become disengaged and require re-attaching around the bar and sprocket. If the chain should become partially disengaged from the saw bar when the cassette is not in use, and if the cassette is then connected in operative position on the chain saw frame, a dangerous situation can arise wherein the saw chain may rapidly disengage from the saw bar.